

A287221


Number of twicecrossing partitions on n nodes.


2



0, 0, 0, 0, 8, 42, 168, 760, 2418, 10490, 30842, 131676
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OFFSET

0,5


COMMENTS

The meandric numbers A005316 are the numbers of paths which cross themselves 0 times.
This sequence is the number of paths that must cross themselves exactly twice.


LINKS

Table of n, a(n) for n=0..11.
B. W. J. Irwin, On the number of kcrossing partitions


EXAMPLE

a(4) = 8; this is from the partitions
(2,1,4,3), (2,4,3,1),
(3,2,4,1), (3,4,2,1),
(4,1,3,2), (4,2,1,3),
(4,2,3,1), (4,3,1,2).


CROSSREFS

Cf. A005316, A287220.
Sequence in context: A231069 A319235 A256861 * A119965 A229729 A055082
Adjacent sequences: A287218 A287219 A287220 * A287222 A287223 A287224


KEYWORD

nonn,more


AUTHOR

Benedict W. J. Irwin, May 22 2017


STATUS

approved



